A multimedia broadcast multicast service (MBMS) means a streaming or background service provided to a plurality of user equipments by using a downlink dedicated MBMS bearer service. An MBMS bearer can be divided into a point-to-multipoint radio bearer service or a point-to-point radio bearer service.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all user equipments (UEs) within a broadcast area. The broadcast area refers to a region where the broadcast service is possible. On the other hand, the MBMS multicast mode is a service for transmitting the multimedia data to a specific user equipment group only within a multicast area. The multicast area refers to a region where the multicast service is possible.
User equipments, which desire to receive a specific MBMS, should perform a subscription procedure. Subscription refers to establishing a relationship between a service provider and a user equipment. Also, the user equipments, which desire to receive the MBMS, should receive a service announcement provided by a network. The service announcement refers to providing the user equipments with a list of services to be provided and related information of the services.
Meanwhile, a user equipment which desires to receive the MBMS of the multicast mode should join a specific multicast group. The multicast group refers to a group of user equipments, which receive a specific multicast service, and joining refers to merging with a multicast group grouped to receive the specific multicast service.
The user equipment can notify the network through the joining that it desires to receive specific multicast data. On the other hand, the user equipment which has joined the multicast group can unsubscribe to joining of the multicast group, which is referred to as leaving. Each user equipment performs the subscription, joining and leaving procedures. The user equipment can perform the subscription, joining, and leaving procedures at any time, such as before data transmission, during data transmission, or after data transmission.
Meanwhile, when the specific MBMS is being performed, one or more sessions can be generated sequentially with respect to the specific MBMS. If data to be transmitted with respect to the specific MBMS are generated in MBMS data source, a core network (CN) notifies a radio network controller (RNC) of session start. On the other hand, if data to be transmitted with respect to the specific MBMS are stopped in the MBMS data source, the core network (CN) notifies the RNC of session stop. Data transfer of the specific MBMS can be performed between session start and session stop. At this time, user equipments (UE), which have joined the multicast group for the specific MBMS, can only receive the data transmitted through data transfer.
During session start, a universal terrestrial radio access network (UTRAN), which has received announcement of session start from the core network (CN), transfers MBMS notification to the user equipments (UEs). In this case, MBMS notification means that the UTRAN notifies the user equipments (UEs) that data transfer of the specific MBMS within a specific cell is upcoming.
The UTRAN can perform a counting procedure to identify the number of user equipments (UEs), which desire to receive the specific MBMS within a specific cell, through MBMS notification. The counting procedure is used to determine whether to establish a point-to-multipoint radio bearer or a point-to-point radio bearer, which provides the specific MBMS.
In order to select the MBMS radio bearer, the UTRAN establishes a threshold value internally. After performing the counting procedure, the UTRAN establishes the point-to-point MBMS radio bearer if the number of user equipments (UEs) existing in a corresponding cell is less than the threshold value. However, if the number of user equipments (UEs) existing in a corresponding cell is more than the threshold value, the UTRAN can establish the point-to-multipoint MBMS radio bearer.
If the point-to-point radio bearer is established for the specific service, all the user equipments (UEs), which desire to receive the specific service, are in RRC connected mode. However, if the point-to-multipoint radio bearer is established for the specific service, all the user equipments (UEs), which desire to receive the specific service, do not need to be in RRC connected mode. Namely, the user equipments (UEs), which are in an idle mode, can receive the specific service through the point-to-multipoint radio bearer.
A medium access control (MAC) entity, which supports MBMS, supports two types of logical channels for MBMS, i.e., a MBMS control channel (MCCH) and a MBMS traffic channel (MTCH).
The logical channel, MCCH is a point-to-multipoint downlink channel, and transmits data of a control plane related to a specific MBMS, i.e., control information to the user equipments. The logical channel, MTCH is also a point-to-multipoint downlink channel, and transmits data of a user plane related to a specific MBMS, i.e., user data to the user equipments.